Haploid organisms contain the same number of chromosomes (n) in their somatic cells as do the normal gametes of the species. The ploidy level of a somatic cell is defined as the number of sets of the haploid number of chromosomes that the cell contains. For example, humans are diploid organisms, having 2 n chromosomes in somatic cells. When the ploidy level is greater than one, it is often difficult to know which genes the organism possesses, due to dominance. When more than one copy of a gene is present only one copy may be expressed, the dominant one. The other copy of the gene, the recessive allele, is said to be masked because its presence is not apparent at the phenotypic level.
The existence of haploid organisms can simplify the process of plant breeding. Due to the absence of dominance effects in haploids, the phenotype is an accurate representation of the genotype. For these and other reasons, which will be apparent to those skilled in the art, the availability of haploids in a particular species can be a powerful tool in a plant breeding program.
Spontaneous haploids occur in many species, albeit at low frequencies. Haploid plants of certain species have also been recovered by various laboratory manipulations, including parthenogenesis, androgenesis, chromosome elimination, and tissue culture methods. However, with few exceptions, the yield of haploids obtained with these techniques is not great enough to be practical for use in a breeding program. Furthermore, the actual technique used, seems to vary from species to species such that a successful protocol for generating haploids in carrot, for example, will not necessarily be successful for pepper.